The invention relates to closure elements such as doors and windows, and to frames for such closure elements, and more particularly to a frame with a sliding mechanism for enabling a closure element within the frame to slide relative to the frame.
The frame may be a window frame for receiving one or more sashes of a sash window assembly, at least one of which can be slid relative to the frame using the sliding mechanism.
Sash window assemblies may comprise a counter balance system to enable the sash to be easily moved relative to the frame. The counter balance reduces the force required to lift the sash with the counter balance connect to the sash via a pulley. When the sash is raised the counter balance drops, such that part of the force required to lift the sash is provided by the counter balance. Similarly when the sash is lowered, an additional force will be required to overcome the weight of the counter balance, thus inhibiting the sash from moving relative to the frame simply under the weight of the sash.
Alternatively a spiral balance system may be used in which a spiral rod with a thread of varying pitch is coupled to a sash. The spiral rod is coupled to a spring, such that when the spiral rod is rotated the spring is compressed, therefore providing a counter force against the weight of the sash during lifting or lowering of the sash.
The spiral balance system may employ an extension spring. The force from the extension spring may not be constant, for example the force to move an extended spring can vary from the force required to extend a compressed spring. The variation in force can lead to an insufficient force from the spring at the extremities of travel of the sash, therefore leading to the sash moving relative to the frame at the top and bottom due to the weight of the sash or force of the spring. The variation of the pitch on the spiral rod leads to a change in the compression of the spring, such that the variation in the force during compression of the spring is accounted for.
The length of travel of the sash for which the weight of the sash window is equal to the force from the spiral spring system is limited, therefore the spiral spring system requires travel stops to prevent overextension of the spring and permanent damage to the spring. Without the use of travel stops, the behaviour of the spring will change due to a deformation of the spring and thus the function of the window assembly will subsequently change.
A window assembly may enable a sash to be rotated out of the plane of the window frame, for example to enable cleaning. An expanding shoe within a track may be used to inhibit the sash from moving in the plane of the frame whilst rotated out of the plane of the frame. The expanded shoe inhibits the movement of the sash by friction with the frictional force increasing as the sash is rotated further. The frictional force may not be sufficient when the sash is partially rotated out of the plane of the frame, leading to slippage of the sash in the plane of the frame and possible misorientation such that one side of the sash drops relative to the other. It can be difficult to rectify the position of the sash to the original aligned or “square” position. If the sash is moved whilst in the misoriented state the sash may rub against the window frame causing damage of the outer edge of the frame and/or sash.
A sash window may use metal arms to arrest the rotation of the sash relative to the frame. Metal arms can lead to additional wear on the frame and/or sash during rotation of the window. Moreover if the sash and the window become misorientated the contact between the metal arms and the frame and/or sash will increase and therefore the rate of wear will increase. The additional wear can remove any protective coating (e.g. paint), this can be unsightly and reduce the protection of the underlying material.